The problem of the optimization of the distribution of a fluid comprised of at least one gaseous phase and at least one liquid phase is already the subject of several solutions which are examined below:
Patent FR 2 745 202 and patent U.S. Pat. No. 5,688,445 thus propose a plate with pipes which are fitted with holes arranged in tiers along the pipe for the passage of the gas (upper holes) and of the liquid (lower holes). No system is provided in this prior art to prevent the fluctuations of the liquid/gas interface above the plate that are due to the injection of the liquid at the top of the reactor. In fact, because of their configuration, any imbalance in this interface necessarily means an imbalance of the gas and liquid fluxes from one pipe to the other, which is clearly harmful to the homogeneity of the mixture.
Patent WO 95/35159 proposes a distribution system on two levels. The first level is comprised of a circular plate with raised edges that is intended to dampen the impact of the gas/liquid flow entering the reactor. The liquid then flows from this first plate towards the distributor plate through tubes the base of which contains slots. These tubes are not under liquid load and a certain quantity of gas can thus flow mixed with the liquid. This first plate must calm the oscillations of the liquid level on the second plate or distributor plate, but the entrainment of the gas at the descent tubes can produce foaming at the liquid guard of the distributor plate and thus degrade the feed of the distribution pipes. The second level is comprised of a plate with pipes that are pierced by holes partly situated above the plate and partly situated below the plate. The drawback of this plate is that the flexibility vis-à-vis the liquid flow rate is achieved using two types of pipes. Depending on the liquid flow rate, the density of the injection points is thus variable. In addition, the introduction of two levels imposes a substantial height at the top of the reactor.
U.S. Pat. No. 4,140,625 proposes a system of plates crossed by venturi flumes. The gas is injected at the top of these flumes and the liquid is injected at the neck or upstream from the convergent zone of the venturi. The gas/liquid mixture is then injected into the catalytic bed. This system has the drawback of offering only a small flexibility as regards liquid flow rate since there is only one level of holes for the liquid.
U.S. Pat. No. 5,799,877 proposes a distributor plate system in which the gas and the liquid are injected through concentric tubes, the tube for injecting the gas being situated in the centre. To guarantee a broad operating range in terms of liquid flow rate, the height of the tubes for the introduction of the liquid is variable according to the injection points. This invention thus has the drawback of proposing a density of points for the injection of the liquid that is variable according to the liquid flow rate. In particular, the smallest liquid flow rates, the very ones which are most difficult to distribute well, benefit from the smallest number of injection points. Secondly, no system is provided to dampen the fluctuations of the liquid level above the plate that would be due to the impact of the gas/liquid flow on entering the reactor.
To summarize, among the systems proposed in these various patents and using a plate with mixed injection of the liquid and gas phases, either the plate offers a great flexibility as regards liquid flow rate but has no means of stabilizing the gas/liquid interface upstream from the plate, or the plate has two levels in order to dampen the fluctuations of the gas/liquid interface, but offers only a small flexibility as regards liquid flow rate.